We have developed and characterized a unique cell-line (K-562) originally derived from a patient with chronic myelogenous leukemia (CML). This CML cell line has the Philadelphia (Ph1) chromosome and is free of Epstein-Barr virus genome, herpes-like virus and mycoplasm and does not have T or B cell markers. Such a cell line, which also can yield sublines with two and three PhI chromosomes not only provides a controlled and reliable source of CML cells free of some common oncogenic viruses, but can also be examined for relative synthesis of specific antigen with respect to the karyotype. These CML cells when injected into rabbits cause the production of specific antibody which demonstrates complement dependent cytotoxicity for CML cells. In preliminary experiments, the cytotoxicity for CML cells is not removed if the serum is absorbed with either leukocytes of granulocytes from normal donors. Absorption with CML cells does effectively remove the cytotoxic activity. Furthermore, the immune serum is not cytotoxic for normal human leukocytes. Other data indicate that the antiserum is cytotoxic for leukocytes from patients with CML obtained prior to treatment or during relapse. The purpose of this project is: 1) to evaluate the specificity of the antiserum and its use as a diagnostic and/or prognostic aid; 2) to isolate and characterize the CML specific antigen(s); 3) to characterize the antibody during the immune response at selected intervals and assess the cytotoxicity on cells from normal and human patients suffering from leukemias, lymphomas and several other hematologic and non-hematologic diseases.